Wheel tracking rutting performance estimation based on bitumen Low Shear Viscosity (LSV), loading and temperature conditions

The development of new technologies and road pavement materials require the evaluation of the asphalt mixture performance. Rutting is one of the main modes of failure of asphalt mixtures; it is typically studied at the laboratory through the wheel tracking test (WTT). Weather and traffic conditions (temperature, loads) significantly affect the pavement rutting performance. The bitumen rheological properties also have a main role in mixture rutting response; they can adequately characterized by the bitumen Low Shear Viscosity (LSV). The estimation of rutting performance appears as a useful decision tool to optimize pavement design process. This paper studies the rutting performance of asphalts mixtures utilising the WTT. The specimens were tested at different temperatures and loading levels to simulate different climatic and traffic pavement conditions. A performance estimator was developed including temperature and traffic load on the pavement, and LSV of the binder as input data.     

Fatigue life and endurance limit prediction of asphalt mixtures using energy-based failure criterion

Fatigue cracking is one of the major types of distress in asphalt mixtures and is caused by the accumulation of damage in pavement sections under repeated load applications. The fatigue endurance limit (EL) concept assumes a specific strain level, below which the damage in hot mix asphalt (HMA) is not cumulative. In other words, if the asphalt layer depth is controlled in a way that keeps the critical HMA flexural strain level below the EL, the fatigue life of the mixture can be extended significantly. This paper uses two common failure criteria, the traditional beam fatigue criterion and the simplified viscoelastic continuum damage model energy-based failure criterion (the so-called G^R method), to evaluate the effect of different parameters, such as reclaimed asphalt pavement (RAP) content, binder content, binder modification and warm mix asphalt (WMA) additives, on the EL value. In addition, both failure criteria are employed to investigate the impacts of these parameters in terms of the fatigue life of the study mixtures. According to the findings, unlike an increase in RAP content, which has a negative effect on the mixtures’ fatigue resistance, a higher binder content and/or binder modification can significantly increase the EL value and extend the fatigue life as was proved before by other researchers, whereas WMA additives do not significantly affect the mixtures’ fatigue behaviour. A comparison of the model simulation results with the field observations indicates that the G^R method predicts the field performance more accurately than the traditional method.     

Investigating the effect of nanoparticles on the rutting behaviour of hot-mix asphalt

Rutting is considered as one of the major damages in asphalt mixtures. In this study, different types of nanoparticles such as TiO₂, Al₂O₃, Fe₂O₃ and ZnO in different percentages were added to the base asphalt binder in order to decrease the rutting potential of hot-mix asphalt (HMA). In the first step, asphalt binder tests for characteristics such as penetration grade, ductility, softening point and viscosity were performed on the asphalt binder modified by the nanoparticles. Then, after preparing HMA samples, the static creep test was done at two stress levels at a specific temperature. Results of this study showed that using the nanoparticles improved the behavioural properties of the asphalt binder and decreased rutting in asphalt mix samples. Furthermore, scanning electron microscope images taken from the asphalt binder samples modified by the nanoparticles demonstrated that these nanoparticles were properly distributed in the asphalt binder space and had a positive effect on the rutting performance of the asphalt mixes.     

Development and calibration of shear-based rutting model for asphalt concrete layers

This study improves a shear-based rutting model for asphalt concrete (AC) layers and calibrates the model with field data. With dynamic modulus-based material parameters, the laboratory rutting prediction model was improved and determined by the wheel tracking test and full-scale accelerated pavement test. Through the field survey on several in-service pavements, the rutting model was calibrated to be applied to AC layers. In the improved rutting prediction model, the ratio of maximum shear stress to shear strength was introduced to combine asphalt material design and pavement structural design. The speed correction coefficient and the new temperature processing method improve the accuracy of the rutting model. The calibrated rutting prediction model proves to be reasonable and accurate in predicting the rutting depth of AC layers.     

The use of asphalt low shear viscosity to predict permanent deformation performance of asphalt concrete

The permanent deformation performance of asphalt concrete is strongly dependent on the rheological properties of the asphalt binder. It has been recognized that the asphalt’s low shear viscosity (LSV) characterizes the mixture’s rutting resistance. At the same time, the pavement temperature is one of the main factors that significantly affect the mixture performance. In this work the rutting performance of mixtures prepared with the same aggregate gradation and different binders [conventional (C), multigrade (M) and polymer modified (PM) asphalts] were evaluated by using wheel tracking tests (WTT) performed at 50, 60, 70 and 80°C; in parallel, the LSV of asphalts were measured at the same temperatures. The relationship between the asphalt’s LSV and rutting, to predict asphalt mixture performance, was discussed and a criterion to consider the effect of LSV is proposed.     

Simulation of unbound material resilient modulus effects on mechanistic-empirical pavement designs

The variability of resilient modulus (M _R) of unbound materials and subgrade due to laboratory test conditions affect pavement performance and designs. The performance-based mechanistic-empirical pavement design guide (MEPDG) is gaining more popularity in recent years for pavement design use. However, limited research efforts have quantitatively studied M _R effects based on ME models. This research targets to evaluate the influences of M _R variability on pavement performance and designs based on the MEPDG performance models. With a normal-distribution of M _R seed values, pavement responses were computed with a layer-elastic analysis model, pavement performance was then predicted using MEPDG models, and design variability was studied via Monte Carlo simulation. Results indicate that the relationship between layer design thickness and M _R varies from almost linear to nonlinear, which is highly dependent on the pavement structure and material properties. For the evaluated specific pavement structure and range of M _R values, the least susceptible is the HMA design thickness as a function of M _R under fatigue with a design Coefficient of Variance (CV) of 7.51 %, while the most susceptible is the base design thickness as a function of M _R also under fatigue with a CV of 54.32 %. The combined effect of both rut depth and fatigue life considering the variability of both base and subgrade results in a design CV of 22.58 % for asphalt layer and 26.08 % for base layer. When using a weaker base layer or a thinner HMA layer, the modeled thickness design CV has changed ?4.19 to 1.14 %.     

Evaluation of low temperature viscoelastic properties and fracture behavior of bio-asphalt mixtures

The overall national emphasis on sustainability in pavement construction has led to the promotion of recycled materials such as reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles. In general, the inclusion of these materials has led to reduced performance at low temperatures leading to thermal cracking. Previous research by the authors showed that the application of bio-binder from swine manure could alleviate the effect of RAP while improving the overall low temperature bulk viscoelastic and fracture properties of the asphalt mixture. The current paper expands on the previous research on bio-modified asphalt mixtures by investigating three additional bio-asphalts produced by introducing wood, miscanthus and corn stover based bio-oils to a neat asphalt. These bio-asphalt mixtures were introduced in both virgin and reclaimed asphalt pavement mixtures to evaluate interaction between the bio-oils and reclaimed asphalt pavement, with a focus on properties related to low temperature pavement performance. Low temperature characterization was conducted using disk-shaped compact tension fracture (DC(T)) and indirect tension (IDT) bulk viscoelastic characterization tests. The IDT test, completed in accordance with AASHTO T-322, evaluated the creep compliance of mixtures at 0, ?12 and ?24 °C to examine the ability of the mixture to relax thermal stress development. The DC(T) test was completed according to ASTM D-7313 to determine the fracture energy of the mixtures at ?12 °C. Test results demonstrate that the bio-asphalt mixtures had superior physical properties in terms of fracture resistance and creep compliance. Furthermore, the effect of increased RAP contents was less detrimental to low temperature properties in the bio-asphalt mixtures as compared to the reference hot-mix asphalt mixture.     

Investigation of asphalt concrete rutting mechanisms by X-ray computed tomography imaging and micromechanical finite element modeling

This paper systematically investigates the changes in asphalt concrete (AC) microstructure caused by full-scale accelerated pavement testing with a heavy vehicle simulator (HVS), using X-ray computed tomography images taken before and after HVS rutting tests. A viscoelastic micromechanical finite element modeling was also used to investigate effects of bitumen mastic and aggregate skeleton properties on shear resistance. The primary purpose was to determine the reasons behind the earlier failure of the rubberized gap graded AC mix used in the test compared to the polymer modified dense graded mix also included in the experiment. Shear related deformation appears to control the long term rutting performance of the test sections while densification was primarily an initial contributor at the very early stages of trafficking. A high concentration of aggregate interlock in the polymer modified mix, as a result of the dense gradation and larger aggregate sizes, appears to have resulted in greater dissipation of shear stresses and therefore greater shear resistance. The lack of this interlocking effect for the rubberized gap graded mix is proposed to have caused the earlier failure on HVS test sections.     

Improvements on asphalt mixtures rutting performance characterization by the use of low shear viscosity

The relationship between the rutting performance of dense asphalt concretes and the low shear viscosity (LSV) of different asphalt binders was analysed in a previous work. A LSV limit was found for the original asphalt to prevent the rutting of the mixtures, and in addition, a model to predict the rutting performance based on the LSV of the asphalt binder was validated. With the aim of amplifying the criterion previously found, the performances of micro and stone mastic asphalt mixtures are studied in this work. Conventional, multigrade and polymer modified asphalts were used as binders. Considering that the properties of original and aged asphalts must be taken into account for a better asphalt binder characterization, LSV measurements on aged asphalts were also done in order to analyse their relationship to the mixtures rutting performance. The micro and stone mastic asphalt mixtures showed a similar behaviour as the dense grade asphalt concrete in the previous study. Regarding the control of rutting, a LSV limit of 500 Pa.s was found for original asphalts, while 2,000 Pa.s was the limit for aged asphalt binders. The model to predict the rutting performance of asphalt mixtures was amplified, incorporating both original and aged asphalt LSVs as appropriate input data.     

Comparison of methods for measuring zero shear viscosity in asphalts

Permanent deformation or “rutting” is a common mode of failure in asphalt pavements. In order to better determine why rutting occurs, current research is focussed on the rheological properties of the asphalt binder. Zero shear viscosity (ZSV) seems to adequately explain how the asphalt binder contributes to the rutting behaviour of the pavement. Still, the measurement of ZSV in a reliable and reproducible way is an open field of discussion. This work looks into the repeatability, benefits and duration of two test methods to measure ZSV: the creep test and frequency sweep test. To account for the influence of the asphalt type, six different conventional and modified asphalts were tested. A statistical analysis was performed to study the variability of each test method and a comparison between both was made.     

Dynamic model and criteria indices of semi-rigid base asphalt pavement

This paper presents a dynamic model of asphalt pavement by considering the characteristics of moving tyre load, visco-elastic performance of material and layered system of pavement. The pavement is defined as an infinite layered system with the tyre load moving at a constant speed, and asphalt concrete (AC) is characterised as a kind of visco-elastic material. Using the spectrum analysis method, a complex tyre load is decomposed into a series of harmonic loads. Based on the frequency characteristics of a linear system, a universal formulation pattern for differential visco-elastic constitutive relations is provided. And then, a model is set up to analyse the dynamic response of asphalt pavement under moving harmonic load, and then to extend to the arbitrary moving load according to the superposition principle of a linear system. The dynamic responses of seven typical semi-rigid base asphalt pavements are analysed using the model. Analysis results indicate that the tensional strain at the bottom of the AC layer and the vertical compression strain at the top of the roadbed are not suitable for key indices of the semi-rigid base asphalt pavement. The shearing strain at the bottom of the AC layer can be taken as a key index to evaluate the fatigue performance, and the vertical compression strain at the top of the pavement surface can be taken as a key index to evaluate pavement rutting, and the vertical shearing strain at the top of pavement surface can be taken as a key index to evaluate top–down crack.     

柔性基层沥青路面车辙性能的影响因素

为解决柔性基层沥青路面车辙问题,采用室内试验和数值模拟对柔性基层沥青路面车辙性能的影响因素进行了研究。结果表明,空隙率是影响柔性基层沥青混合料抗车辙能力最关键的因素,宜为4%左右;级配形成骨架嵌挤结构能明显提高柔性基层混和料的抗车辙能力,但级配不宜太粗;对SBS改性沥青,可根据基质沥青的高温性能指标来选择改性沥青;温度、荷载、行车速度对柔性基层沥青路面车辙性能有显著影响。     

Influence of selected WMA additives on viscoelastic behaviour of asphalt mixes and pavements

Warm mix asphalt additives are effective in decreasing production, laying and compaction temperatures of asphalt mixes. However, there are still questions concerning influence of warm mix additives on properties of asphalt mixes and pavement performance. This paper presents results of the comprehensive research of viscoelastic behaviour of asphalt mixes and pavement structures with layers made with warm mix asphalt additives at high temperatures. Two additives of significantly different effects on mixes at higher temperatures were selected for analysis, namely aliphatic synthetic wax produced with the use of Fisher–Tropsch method and formulation of surfactant- based molecules (ionic and non-ionic). Viscoelastic properties of mixes with these two additives and, as a reference mix, with neat unmodified asphalt binder were determined in uniaxial compression with sinusoidal loading using Asphalt Mixture Performance Test. The viscoelastic analysis of pavement structures was performed with use of the VEROAD software and data from laboratory testing. Two different pavement structures were analysed, for light and heavy traffic. The temperature distribution in pavement structure during the hottest summer day in northern Poland in 2012 was taken into account. The model of pavement was loaded with moving wheel at different speeds. The analysis has shown that two tested warm mix additives had different effect on viscoelastic transient response at high temperatures. One of them (Fischer–Tropsch wax) evidently caused an increase in resistance of asphalt mix and pavement structure to loading at high temperature. The second additive (formulation of surfactant-based molecules) slightly reduced resistance of asphalt mix and pavement to loading at high temperatures as compared with the reference mix.     

Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder’s contribution to mixture fatigue and pavement fatigue cracking performance.     

A rheological study on aged binder rejuvenated with Pongamia oil and Composite castor oil

Recycling of highway materials is an effort to preserve the natural environment, reduce waste and provide a cost-effective way for construction of highways. The reclaimed asphalt pavement (RAP) contains stiffened binder caused by loss of volatile materials and oxidation. Hence, the addition of high amount of the RAP to asphalt mix may make it prone to fatigue failure. Due to this reason, addition of RAP to asphalt mixture in substantial amount has been a challenge so far. Therefore, ‘rejuvenators’ which are supposed to restore chemical and physical properties of the aged asphalts are used effectively in asphalt mixture. In this study, two locally available oils, i.e. pongamia oil (locally known as Karanja oil) derived from the seeds of Pongamia pinnata and a composite rejuvenator made of castor oil and coke oven gas condensate have been explored for rejuvenating the aged binder. The rheological properties of aged binder and rejuvenated binders were studied using a dynamic shear rheometer. From the various rheological tests conducted, it was found that certain proportion of pongamia oil as well as composite castor oil was able to impart desirable rutting as well as fatigue performance for the rejuvenated binder samples. The thermal analysis carried out using thermogravimetric analysis ensured adequate thermal stability for the binder specimens treated with these oils. In terms of binder performances, it was found that these oils could be considered as suitable rejuvenators for effectively restoring properties of the aged binder. Performance studies on RAP mixes may be extended for recommending these two oils as rejuvenators for hot mix pavement recycling.     

Reconsideration of the fatigue tests for asphalt mixtures and binders containing high percentage RAP

When applying reclaimed asphalt technology in a flexible pavement project, most performance concerns are related to low temperature and fatigue cracking since the stiffness of the HMA mixture could dramatically increase through adding a high percentage of reclaimed asphalt pavement (RAP) material. The purpose of this study is to evaluate asphalt mixtures with high RAP contents, prepared using two RAP addition methods, for their performance based on fatigue-cracking resistance rather than relying on volumetric properties. Asphalt mixture samples were prepared with three RAP binder content replacement percentages (30, 40 and 50%) using two preparation methods: the as-is RAP gradation (traditional method) and the splitting of the RAP gradation into coarse and fine fractions (fractionated method). Asphalt mixture beam fatigue and binder fatigue time-sweep tests were performed. Beam fatigue samples also underwent freeze–thaw cycling for freeze–thaw damage evaluation. Rather than basing the performance based solely on S–N_f curves to illustrate the fatigue performance, the beam fatigue test data was analysed through a dissipated energy approach. Faster fatigue degradation was observed for the 40% RAP binder and beam mixture when subjected to repeated loading. From a morphology aspect, this can be explained by the binder’s phase separation and physical hardening effects.     

Asphalt concrete rutting predicted using the PEDRO model

This paper presents a theoretical viscoelastic approach, called PEDRO (PErmanent Deformation of asphalt concrete layers for ROads), for predicting rut formation in asphalt concrete materials subjected to traffic loading. Input data are traffic parameters, asphalt concrete viscosity and asphalt layer thickness. Vertical strains that cause rutting in the pavement were estimated using the PEDRO approach. A large-size type of wheel tracking machine, which has the capability to subject asphalt concrete slabs to different loadings, has been used to study the effects of wheel load and tyre pressure. Rut development in the slabs under various loading conditions was predicted. The approach has shown reasonable results as regards predicting densification and shear rutting in the tested asphalt concrete slabs.     

Viscoelastic–plastic damage model for porous asphalt mixtures: Application to uniaxial compression and freeze–thaw damage

Porous asphalt mixture increasingly used in highway pavement applications is an open graded composite material which has fewer fines and more air voids compared with conventional dense graded asphalt mixtures. The freeze thaw resistance of the mixture is crucial for the performance of porous asphalt pavement especially when clogging is unavoidable. A simple viscoelastic–plastic damage model is developed to evaluate the effects of freeze–thaw of porous asphalt mixtures. Generalized Maxwell and Drucker–Prager model are used to determine the viscoelastic and plastic responses respectively. The damage and its evolution is characterized by Weibull distribution function. Experimental data from uniaxial compressive strength tests, conducted at different strain rates and temperatures, are used to calibrate the model. The sensitivity of model parameters to loading conditions is identified. Simulation results suggest that loss of cohesion is the dominant mechanism of failure in porous asphalt mixtures under freeze–thaw cycles. Freeze–thaw effects also lead to changes of plastic potential surface and induce large volumetric strains under loading.     

包装废聚乙烯改性沥青路用性能研究

以回收的包装废弃聚乙烯作为改性剂,对普通道路沥青进行改性,并通过沥青混凝土马歇尔试验实验、车辙实验、抗弯强度试验等,对改性后沥青的路用性能进行了研究,结果表明:包装废聚乙烯改性沥青的稳定性、抗弯强度提高、抗车辙能力增强,沥青路用性能得到明显改善.     

The effect of loading time on flexible pavement dynamic response: a finite element analysis

Dynamic response of asphalt concrete (AC) pavements under moving load is a key component for accurate prediction of flexible pavement performance. The time and temperature dependency of AC materials calls for utilizing advanced material characterization and mechanistic theories, such as viscoelasticity and stress/strain analysis. In layered elastic analysis, as implemented in the new Mechanistic-Empirical Pavement Design Guide (MEPDG), the time dependency is accounted for by calculating the loading times at different AC layer depths. In this study, the time effect on pavement response was evaluated by means of the concept of “pseudo temperature.” With the pavement temperature measured from instrumented thermocouples, the time and temperature dependency of AC materials was integrated into one single factor, termed “effective temperature.” Via this effective temperature, pavement responses under a transient load were predicted through finite element analysis. In the finite element model, viscoelastic behavior of AC materials was characterized through relaxation moduli, while the layers with unbound granular material were assumed to be in an elastic mode. The analysis was conducted for two different AC mixtures in a simplified flexible pavement structure at two different seasons. Finite element analysis results reveal that the loading time has a more pronounced impact on pavement response in the summer for both asphalt types. The results indicate that for reasonable prediction of dynamic response in flexible pavements, the effect of the depth-dependent loading time on pavement temperature should be considered.